The present invention relates to a reflector for a vehicular lamp having a rectangular front view.
Among vehicular headlights, fog lamps, etc. are ones that are rectangular when viewed from the front side. FIGS. 12 and 13 show a reflector a as an example of such a type. As shown in FIG. 12, the reflector a consists of a reflecting portion b and walls c surrounding it. (FIG. 12 shows right and left side walls.) As shown in FIG. 13, when viewed from the front side, the reflector a has a rectangular shape that is long in the horizontal direction.
A circular bulb fixing hole d is formed at a, center portion of the reflecting portion b. The optical axis passing through the center O and extending in the front-rear direction is selected as the x-axis. The y-axis is perpendicular to the x-axis and extends in the horizontal direction, and the z-axis is perpendicular to the x-axis and extends in the vertical direction.
A reflecting surface e, which is the inside surface of the reflecting portion b, may have a shape as disclosed in, for instance, Japanese Patent Application Unexamined Publication No. Sho. 50-127487. The reflecting surface e is more diffusive in the horizontal direction than a paraboloid-of-revolution reflecting surface. That is, as indicated by light rays 1 in FIG. 12, a light ray emitted from a point light source located at a focus F on the optical axis and reflected at a point on the reflecting surface e more distant from the optical axis is more diffused, i.e., goes away from the optical axis at a higher rate.
However, the above reflector a is associated with various problems as exemplified below. As indicated by light rays m in FIG. 12, rays reflected at points on the reflecting surface e close to the side walls c are again reflected by the side walls c, and may cause glare. Since the effective area of the reflecting surface e is narrowed to an area A shown in FIG. 12 (that is, rays reflected by an area B are ineffective), it is difficult to further increase the horizontal diffusion.
The above problems result from the fact that a light ray originating from the focus F and reflected at a point on the reflecting surface e more distant from the optical axis is more diffused in the horizontal direction. In order to reduce the ineffective area B, the right and left side walls c need to be inclined greatly with respect to the vertical plane including the optical axis.
Further, since rays reflected by the area A are diffused in the horizontal direction without crossing the optical axis, if the bulb fixing hole d occupies a large area relative to the reflecting surface area, the light quantity may be lowered at a central portion of the light distribution pattern.
FIG. 14 schematically shows how this problem occurs. In FIG. 14, H--H and V--V represent a horizontal line and a vertical line, respectively, and o represents an intersecting point of those lines. Character f represents two relatively bright regions extending along the horizontal line H--H which are projected by respective areas obtained by halving the reflecting surface e by the vertical plane including the optical axis. A portion D (indicated by a dashed line in FIG. 14) located in the vicinity of the point o and between the regions f tends to be relatively dark due to the influence of the bulb fixing hole e.